The present disclosure pertains to methods and devices for ascertaining the efficacy of one or more preservatives present in materials to prevent the growth of microorganisms. More particularly, the present disclosure pertains to methods and devices that can determine the efficacy and/r effectiveness of one or more preservatives present in a manufactures product in preventing or retarding the growth of microorganisms in the product.
For various manufactured products, such as cosmetic and toiletry products, a certain microbiological test Preservative Efficacy Test (PET) can be carried out to determine the efficiency of specific preservatives designed to prevent growth of microorganisms such as bacteria, yeasts and molds. Unlike regular microbiological tests (assays) that determine the presence or absence of microorganisms in a product, the PET “challenges” the product by intentionally inoculating a sample of the product with living microorganisms, and testing microorganism concentration after predetermined exposure times in order to determine whether the preservative is efficient in eliminating the microorganisms or significantly reducing their numbers.
Use of certain manufactured products contemplates repeated contact between the product and potential contamination sources. For example, many cosmetic and toiletry products such as foundations, creams, sun tan lotion, mascara and lipstick involve application techniques in which the consumer frequently touches the products in the container to obtain an application portion. This process can inadvertently introduce microorganisms to the product. In many instances, one or more preservatives are added to the product to eliminate introduced microorganisms and/or prevent or reduce microorganism proliferation. Ascertaining the efficacy of one or more of these preservatives at reducing or eliminating proliferation of undesired microorganisms that can be introduced during product use. The efficacy test is essential to verify that the product would not develop into microbiological hazard to its user.
Preservative efficacy tests (also called antimicrobial challenge tests or antimicrobial effectiveness testing) are currently performed using the traditional plate count method in which the tested product is inoculated with the microorganisms which are allowed to incubate in the product for predetermined amount of time. Thereafter the product is diluted in a neutralizing solution to eliminate the effect of the preservative in order to enable subsequent growth of the surviving microorganisms. The number of the surviving microorganisms is counted on the Petri-dish plates to determine the effect of the preservative. In the Petri-dish plate method, decimal dilutions of the neutralized inoculated product are prepared. Each decimal dilution is introduced into Petri-dish plates equipped with agar and appropriate growth media. The resulting inoculated Petri dish plates containing the agar, growth medium and an associated inoculated decimal dilution sample is are each incubated for several days enabling any surviving microorganisms to grow into colonies and which are counted.
Where the inquiry is the efficacy of the preservative after elapsed time after exposure, the efficacy test just outlined can be performed in a way that provides insight into efficacy over time. In many instances, the Petri dish method and the process just outlined is repeated for several different predetermined exposure time intervals. In certain scenarios, exposure times of one or more of the following: 7 days, 14 days, 21 days, 28 days can be employed with successful efficacy test results typically being when fewer organisms survive whenever the inoculated product is exposed to the preservative(s) as time progresses.
The Petri dish test method as outlined is also used to determine which preservative and preservative concentration provides effective protection without causing side effects to the product or to the consumer. U.S. Pharmacopeia, Chapter 51 specifies that preservative efficacy testing be conducting against various microorganisms including but not limited to the following microorganisms: Candida albicans (ATCC No. 10231), Aspergillus brasiliensis (ATCC No. 16404), Escherichia coli (ATCC No. 8739), Pseudomonas aeruginosa (ATCC No. 9027), and Staphylococcus aureus (ATCC No. 6538).
The traditional Petri dish efficacy test method outlined above has numerous drawbacks. The traditional Petri dish efficacy test method is a complicated multi-step method that requires extensive manual manipulation and labor. In typical cosmetic or toiletry manufacturing facilities, thousands of Petri dish plates must be individually inoculated and individual placed in incubators. Each plate has to be monitored as it incubates for its specific period of time. After incubation, the microorganism colonies that have been produced as a result of microorganism growth must be counted and the results for each Petri dish plate must be manually recorded. Both the counting operation and the recording operation are opportunities for error. Additionally, final analysis is required to verify that the reduction of organisms over time (expressed in logarithmic scale) complies with predetermined standard values specific to each combination of product, organism and progressing exposure days. Thus, it would be desirable to provide a method and device that could reduce or minimize manual operations associated with efficacy testing without compromising accuracy or efficiency. Additionally, the Petri dish method as outlined above does not effectively permit dynamic analysis of microorganism growth.